D M Collins

Bio: D M Collins is an academic researcher. The author has contributed to research in topics: Embedment & Deflection (engineering). The author has an hindex of 2, co-authored 2 publications receiving 70 citations.

Load-deflection behavior of cast-in-place and retrofit concrete anchors subjected to static, fatigue, and impact tensile loads. interim report

Abstract: The purpose of this study was to investigate the design and behavior of single cast-in-place and retrofit concrete anchors under static, fatigue, and impact tensile loads. The following types of anchors were tested: (1) Cast-in-place anchor bolts and embeds; and (2) Retrofit anchors--(a) adhesive anchors (epoxy, polyester, and vinylester); (b) grouted anchors; (c) expansion anchors (torque-controlled); and (d) undercut anchors. The study described in this report involved 178 tests. Load-deflection behavior was recorded for each test. Behavior of adhesive anchors was studied with respect to variations in installation, orientation (vertical, horizontal, and overhead), and in hole cleaning techniques. Most anchors had a 5/8-in. nominal diameter. Required embedment lengths for the cast-in-place anchors were estimated using the criteria of ACI 349 Appendix B. Embedment lengths for the embeds, expansion, undercut, and some adhesive anchors were determined by the individual anchor manufacturer, and some anchors were only available in fixed lengths. Behavior modes of anchors were identified under static, fatigue, and impact tensile loads, and anchor types were categorized according to these behavior modes. Recommendations are given for embedment depths and installation techniques for anchors of each type. Recommendations are made for further research, some of which will be addressed in future reports produced by this project.

Load-deflection behavior of cast-in-place and retrofit concrete anchors

Abstract: This is an investigation for the design and behavior of single cast-in-place and retrofit concrete anchors under static, fatigue, and impact tensile loads The embedment lengths used in this study were designed to produce ductile behavior, which was defined as steel failure of the anchor shank Anchor types tested were cast-in-place anchor bolts and embeds and four types of retrofit anchors: adhesive; grouted; expansion; and undercut The study compared the design, load deflection behavior and mode of failure of retrofit concrete anchors with that of cast-in-place anchors under different tensile loading conditions Behavior modes of anchors were identified under static, fatigue, and impact tensile loads, and anchor types were categorized according to these behavior modes

Behavior of Chemically Bonded Anchors

Abstract: Bonded anchors are frequently used in both new construction and repair or retrofit projects. Current design standards do not contain rational design recommendations for these anchors. This paper presents rational design recommendations for evaluating the tensile strength of bonded anchors. The design recommendations account for all typical embedment failure modes observed in tension tests (i.e., concrete cone failure, bond failure, and the more common combined cone‐bond failure mode). The design recommendations presented are based on a behavioral model derived from elastic theory, on a combined cone‐bond failure model that predicts cone depth, and on the results of a total of 280 tests conducted at the University of Florida (167 tests) and the University of Texas (113 tests). The anchor strengths predicted from the design recommendations are compared to test results.

Tensile Behavior of FRP Anchors in Concrete

Abstract: Strengthening of concrete structures using fiber-reinforced polymer (FRP) systems has become a widely accepted technology in the construction industry over the past decade. Externally bonded FRP sheets are proven to be a feasible alternative to traditional methods for strengthening and stiffening deficient reinforced or prestressed concrete members. However, the delamination of FRP sheets from the concrete surface poses major concerns, as it usually leads to a brittle member failure. This paper reports on the development of FRP anchors to overcome delamination problems encountered in surface bonded FRP sheets. An experimental investigation was conducted on the performance of carbon FRP anchors that were embedded in normal- and high-strength concrete test specimens. A total of 81 anchors were tested under monotonic uniaxial loading. Test parameters included the length, diameter, and angle of inclination of the anchors and the compressive strength of the concrete. The experimental results indicate that FRP ...

Headed steel stud anchors in composite structures, Part II: Tension and interaction

Abstract: The 2005 AISC Specification for Structural Steel Buildings is the leading specification for composite construction in the US. However, these provisions do not provide a recommendation for computing the strength of headed steel stud anchors (traditionally used as shear connectors) under tension or combined tension and shear. Headed stud anchors are subjected to these types of forces in composite structures such as infill walls, composite coupling beams, the connection region of composite columns, or composite column bases. While the ACI 318-08 Building Code, the PCI Handbook, 6th edition, and CEB Design of Fastenings in Concrete include provisions for such conditions, those provisions are geared for more general anchorage conditions than are typically seen in composite construction. It would thus be beneficial to have design guidance specifically for the case of headed steel stud anchors subjected to tension or combined tension and shear in composite construction, evaluated within the context of the AISC and EC-4 Specifications. In this work, different strength equations to compute the nominal tensile strength of a headed stud are reviewed and compared to experimental results. The resulting recommendations seek to ensure a ductile failure in the steel shank instead of a brittle failure within the concrete. Several criteria are proposed to ensure that ductile failure controls in composite construction, and, different headed stud configurations and detailing reinforcement recommendations are proposed to improve the ductile behavior of headed stud anchors subjected to tension and combined tension and shear.

Pullout simulation of postinstalled chemically bonded anchors

Abstract: Chemically bonded postinstalled anchors have seen tremendous growth over the past few years for retrofits, as well as new construction. Currently, they are designed from proprietory tables provided by adhesive manufacturers based on laboratory pullout tests. Recently, Doerr et al. in 1989, Cook in 1993, and Eligehausen et al. in 1984 have developed equations to predict pullout resistance of anchors. Since chemically bonded anchors result in the failure of both the concrete and adhesive-concrete interface, the equations attempt to predict the ultimate resistance of the anchor through the sum of the contributions from the concrete-failure cone and adhesive-concrete interface. However, this approach requires an estimate of both the average or maximum shear stress within the adhesive bond layer and the concrete-failure cone depths. To shed more light on the development of failure for these types of anchors, a state-of-the-art elastoplastic finite-element analysis was performed and compared to experimental results. Besides being able to predict pullout resistance, concrete-failure cone depths, and orientations, the analysis revealed that failure initiates as a tension zone below the concrete surface at the anchor-adhesive interface and propagates with load toward the surface. In the process, both the concrete and adhesive material dilate increasing the confinement and shear resistance within the adhesive layer. Once the tension zone reaches the surface, the confinement is lost, resulting in a diminished shear resistance within the adhesive layer and anchor failure. After comparing a number of proposed methods to predict resistance to the experimental data, it was found that a simplistic, uniform bond stress applied over the whole anchor did an excellent job of predicting pullout capacity.

Concrete breakout strength of single anchors in tension using neural networks

Abstract: A feed forward neural network model for evaluating the concrete breakout strength of single cast-in and post-installed mechanical anchors in tension is presented. The nodes of the neural network input layer represent the embedment depth, anchor head diameter, concrete strength and anchor installation system, and the neural network output is the tensile capacity of anchors as governed by the concrete breakout. Three different techniques have been adopted to represent the anchor installation system in the neural network input layer. The training, validation and testing of the developed networks were based on a database of 451 experimental tests obtained from previous laboratory anchor tests. Testing of the trained neural network indicates good predictions of the concrete breakout strength of cast-in and post-installed mechanical anchors in tension.The relationships between the concrete breakout strength of anchors and different influencing parameters obtained from the trained neural networks were in general agreement with those of the ACI 318-02 for cast-in and post-installed mechanical anchors. It has been shown that the concrete breakout strength of anchors in tension is approximately proportional to the embedment depth of 1.5 power and marginally affected by changing the anchor head diameter.